Microlens, its forming method and optical module

ABSTRACT

A method for forming many microlenses comparatively easily and effectively is provided. On one end of an optical substrate is formed a plurality of lens planes at regular intervals. Lens areas containing the lens planes are partially covered by an etching mask and etching processing is performed on areas being exposed outside the etching mask to remove the areas to a specified depth. While the lens planes formed on one surface of the optical substrate are being held by a support substrate, polishing processing is performed on another end face of the optical substrate and each microlens formed in the lens areas is separated from the support substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a microlens and its forming methodbeing suitably used in devices for optical communications and moreparticularly to the microlens and its forming method being suitablyapplied to formation of many very fine and small diffractive opticalelements such as computer-generated hologram (CGH) devices.

2. Description of the Related Art

A method for forming many microlenses each being coupled to an opticalfiber is disclosed in “Proceeding SPIE (Vol. 3631, p234-243)” issued inApril 1999. According to this conventional technology, by tying manycylindrical optical elements each having an outer diameter equal to thatof an optical fiber in a bundle and by performing etching processing onend faces of the optical elements using specified etching mask, manyspecified lens planes can be formed on an end face of each of the manyoptical elements in a collective manner.

By using the microlens made from such the optical element having thesame outer diameter as that of the optical fiber, when the microlens isplaced in a V-groove on a substrate in a manner that an end face of alens plane faces an end of the optical fiber being also placed in theV-groove, it is possible to accurately align an optical axis of themicrolens with that of the optical fiber.

However, the conventional method for forming the microlens describedabove has problems. That is, in the conventional method, in order tocollectively form the lens plane on end faces of many optical elements,it is necessary to surely and accurately tie many optical elements in abundle, however, it is not easy to accurately tie many optical elementsin a bundle and to reliably form the lens plane on the end faces of themany optical elements.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a method for forming many microlens comparatively easily andeffectively. It is another object of the present invention to provide anovel microlens which enables exact alignment of an optical axis of themicrolens with an optical axis of the optical fiber.

According to a first aspect of the present invention, there is provideda method of forming a plurality of microlenses including the steps of:

forming a plurality of lens planes on one surface of an opticalsubstrate;

forming a plurality of mask portions respectively on each the lensplanes;

forming lens element portions which has the lens plane and becomesmicrolens respectively under each of the mask portions by an etchingprocess conducted on the optical substrate;

removing all mask portions;

holding these lens element portions by a holding means from the side theone surface of the optical substrate is located;

removing a remainder of the optical substrate excluding these lenselement portions for leaving these lens element portions by a removingprocess;

eliminating the holding means from all lens element portion by aeliminating process.

With the above configuration, after forming collectively and integrallya plurality of lens element portions each containing a lens plane by theetching process and others conducted on an optical substrate having aplurality of lens planes, separating these lens element portions by theremoving process and the eliminating process. Therefore, a plurality ofmicrolenses each made up of the lens element portions is formed easilyand effectively.

In the foregoing, the etching process may be an etching processing toetch an exposure area portion being not covered by these mask portions.

Also, the etching process may contain a etching processing to etch anexposure area portion being not covered by these mask portions forforming a part of the lens element portion, a forming processing to forma protecting film on a wall surrounding face of the part formed by theetching processing, and a film removing processing conducted after alllens element portions are formed by conducting the etching processingand the forming processing repeatedly to remove the protecting film.

Also, the etching process may be conducted by using etching gasexhibiting an anisotropic etching characteristic.

With the above configuration, it is possible to provide a desired lengthto each microlens.

In the method, the optical substrate may be made up of a crystalsubstrate, the crystal substrate may be a silicon crystal substrate.When using the silicon crystal substrate, the removing process may be apolishing processing.

Also, in the method, the optical substrate may be SOI substrate. It hasa silicon layer having the one surface and providing a thickness incorrespondence with a length of the microlens, a silicon dioxide layerfixed on the silicon layer, and a silicon substrate layer fixed on thesilicon dioxide layer. When using the SOI substrate, the removingprocess is a dissolving processing to dissolve said silicon dioxidelayer.

In the method, the holding means may consist of a wax material layerused to fill the space between these lens element portions and coveringall lens element portions, and a holding substrate fixed on the waxmaterial layer. When using the holding means, the eliminating process isa dissolving processing to dissolve the wax material layer.

In the method, the microlens may be a diffractive optical element, inthis case, the lens plane of the diffractive optical element is formed.

Also, in the method, moreover the steps may be comprised that are toform a antireflection film on each of end faces of all lens elementportions which is located on an opposite side of the lens plane afterfinishing the removing process, to use a support means to support alllens element portions from the side all the end faces are located onwhich the antireflection film is formed before conducting theeliminating process, to form a antireflection film on all lens planes ofall lens element portions after finishing the eliminating process, andto remove the support means from all lens element portions by conductinga support means eliminating process.

The support means may have a support substrate to support all lenselement portions through UV (Ultraviolet) resin layer, said supportmeans eliminating process is a dissolving processing to dissolve the UVresin layer.

Also, there is provided a method of forming a plurality of microlensincluding the steps of:

forming a plurality of lens planes on one surface of an opticalsubstrate;

forming a plurality of mask portions respectively on each of the lensplanes;

forming lens element portions which has the lens plane and becomes themicrolens respectively under each of the mask portions by an etchingprocess conducted on the optical substrate;

forming a mold by using the optical substrate as an original substrateobtained after all the mask potions are removed for reproducing theoptical substrate

forming replica substrates by using the mold;

holding all lens element portions of the replica substrate by a holdingmeans from the side one surface of the replica substrate is located;

removing a remainder of the replica substrate excluding these lenselement portions for leaving these lens element portions by a removingprocess;

eliminating the holding means from all lens element portions by aeliminating process.

According to a second aspect of the present invention, there is provideda microlens formed by methods stated above, wherein the microlens isplaced in series to face an optical fiber in a V-groove on a substrate,and it has an outer diameter in correspondence with that of said opticalfiber and a lens plane facing the optical fiber.

Also, there is provided a microlens formed by a method stated above,wherein the microlens is substantially a cylindrical shape as a whole,and has one end face on which the lens plane is formed and another endface which is opposed to the one end face.

Also, there is provided an optical module including:

a microlens stated above, an optical fiber having an outer diameterbeing substantially same as that of the microlens, and a substratehaving a groove

wherein the microlens and the optical fiber are placed in the groove inseries, and the lens plane of the microlens faces one end face of theoptical fiber.

Also, the groove may be V-groove.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the presentinvention will be more apparent from the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a process diagram illustrating a method for forming amicrolens according to a first embodiment of the present invention;

FIG. 2 is a perspective view showing an example in which the microlensformed by the method of the first embodiment of the present invention isused;

FIG. 3 is a process diagram showing one example of a method for forminga lens plane of the microlens according to the first embodiment;

FIG. 4 is a process diagram (1) illustrating a method for forming amicrolens according to a second embodiment of the present invention;

FIG. 5 is also a process diagram (2) illustrating the method for formingthe microlens according to the second embodiment of the presentinvention;

FIG. 6 is a process diagram illustrating a method for forming amicrolens according to a third embodiment of the present invention; and

FIG. 7 is a process diagram illustrating a process of forming anantireflection film for the microlens according to the third embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Best modes of carrying out the present invention will be described infurther detail using various embodiments with reference to theaccompanying drawings.

First Embodiment

FIG. 1 is a process diagram illustrating a method for forming amicrolens according to a first embodiment of the present invention.Prior to description of the method for forming the microlens of thefirst embodiment, an example in which the microlens formed by the methodof the first embodiment is used will be explained by referring to FIG.2.

The microlens 10 formed by the method of the present invention is usedas an optical element, for example, for optical communications. FIG. 2shows an example of optical module using the microlens. In the exampleshown in FIG. 2, the microlens 10 is placed on a semiconductorsubstrate, for example, silicon substrate 11 serving as a supportsubstrate and is used to gather signal light emitted from an opticalfiber 12 at a specified place or to gather signal light emitted from alight source such as a laser diode (not shown) and to guide the gatheredlight into the optical fiber 12 and, thus, the microlens 10 is used incombination with the optical fiber 12.

As the semiconductor substrate 11, for example, a silicon substrate isemployed. On the substrate is formed, by using an etching method, aV-groove 13 used for positioning of the optical fiber 12. In the exampleshown in FIG. 2, the cylindrical microlens 10 having an opticalcharacteristic to gather light emitted from the optical fiber 12 at aspecified place, is arranged in the V-groove 13 on the substrate 11 in amanner that its lens plane 10 a faces an end face of the optical fiber12.

The optical fiber 12 is a single mode optical fiber having an outerdiameter of 125 μm adapted to guide signal light having a wavelength of,for example, 1.3 μm or 1.5 μm, and the microlens 10 is placed in theV-groove 13, with its optical axis being aligned with that of theoptical fiber 12, so that it can be coupled optically to the opticalfiber 12.

The microlens 10 is made up of a cylindrical optical element having anouter diameter of, for example, 125 μm being equal to an outer diameterof the optical fiber 12 and a height of 100˜200 μm. The microlens 10 maybe made up of an optical material such as silica or silicon if lighthaving a wavelength of 1.3 μm or 1.5 μm described above is handled, andthe lens plane 10 a of the optical element is formed at an end face ofthe optical element to obtain a desired optical characteristic.

By forming the microlens 10 so that its outer diameter matches that ofthe optical fiber 12 and by placing the microlens 10 and the opticalfiber 12 in the V-groove 13, easy alignment of the optical axis of themicrolens 10 with that of the optical fiber 12 can be implemented withhigh accuracy.

Next, the method of collectively forming many microlens 10 will beexplained by referring to FIG. 1. As an optical substrate on which themicrolens 10 is formed, a silicon crystal substrate (for example, asilicon wafer or a like) 14 having a thickness of, for example, 600 μmis employed. On a surface 14 a of the silicon crystal substrate 14, asshown in FIG. 1(a), many lens planes 10 a each exhibiting a desiredoptical characteristic of the microlens 10 are formed at regularintervals.

The many fine and small lens planes 10 a having a diameter of, forexample, of 125 μm can be formed by using photo-lithography and etchingtechnology being applied to Si LSI manufacturing process. That is, byperforming etching processing on the surface 14 a of the silicon crystalsubstrate 14, many lens planes 10 a each exhibiting a desired opticalcharacteristic can be collectively formed with high accuracy.

As shown by a chain line in FIG. 1(a), after a photoresist layer 15 tocover the surface 14 a of the silicon crystal substrate 14 has beenformed, selective exposing processing is performed on the photoresistlayer 15 using a photomask (not shown) corresponding to the lens plane10 a. By the processing of development following the selective exposureprocess, as shown in FIG. 1(b), a plurality of mask patterns 15 a, thatis, as mask portions made up of the photoresist covering each lens plane10 a are formed.

After the formation of the plurality of mask patterns 15 a, by selectiveetching processing using these mask patterns 15 a as an etching mask, asurface area of the substrate 14 being not covered by these maskpatterns 15 a is etched to a specified depth “D”. After the etchingprocessing, as shown in FIG. 1(c), the etching mask, that is, these maskpatterns 15 a are removed.

Then, a wax material 16 as wax material layer is put on the surface 14 aof the silicon crystal substrate 14 in a manner that it covers each ofthe lens planes 10 a being exposed by the removal of these mask patterns15 a and that it fills in concave portions among the lens planes 10 a,as shown in FIG. 1(d). Next, by pressing s support substrate 17 on thewax material 16, as shown in FIG. 1(e), lens areas each containing alens plane 10 a, that is, lens element portions (10) are supported,through the wax material 16, by the support substrate 17. The waxmaterial 16 and the support substrate form a holding means.

As the wax material 16, polishing wax being widely used to support lensmaterials at a time of polishing optical lenses may be employed.Moreover, as the support substrate 17, a support plate such as asemiconductor substrate or a glass plate can be used as appropriate.

Polishing processing such as a chemical mechanical polishing process isperformed on a rear face 14 b of the silicon crystal substrate 14, withthe lens element portions (10) being supported through the wax material16 by the support substrate 17. By the polishing processing, as shown inFIG. 1(f), the silicon crystal substrate 14 excluding the lens elementportions 10 is removed. The polishing processing is continued until thewax material 16 existing among lens element portions (10) is exposed.

After the completion of the polishing process, the wax material servingto hold each of the lens element portions (10) at the support substrate17 is dissolved by using an organic solvent such as, for example,isopropyl alcohol, so that all the lens element portions 10 areseparated from the support substrate 17, that is, many microlenses 10each having the lens plane 10 a are collectively formed.

Each microlens 10 is substantially a cylindrical shape as a whole, andhas one end face on which the lens plane 10 a is formed and another endface which is opposed to the one end face, as shown in FIG. 2.

By using the method of manufacturing the microlens 10 described abovebased on the photo-lithography and etching technology being used in SiLSI manufacturing process, many fine and small microlenses 10 can becollectively formed with high accuracy.

FIG. 3 shows one example in which a method for forming a lens plane ofdiffractive optical elements utilizing a diffraction phenomenon isapplied to the method of forming the lens plane 10 a described above. Inthe method for forming the lens plane of diffractive optical elements,as is conventionally well known, by obtaining a pattern of a photomaskrequired for acquiring a desired optical characteristic from an opticalpath difference coefficient of an optical element exhibiting the desiredoptical characteristic using a computer and by performing etchingprocessing using the obtained pattern on an optical substrate, thediffractive optical element having the desired characteristic can beproduced.

In the example shown in FIG. 3, a method for forming a four-phase lensplane to be obtained by combination of two pieces of the mask patternsis presented. Moreover, in the FIG. 3(a) to (f), a side of a face of thesilicon crystal substrate 14 where the lens plane 10 a is formed ispartially shown.

As shown in FIG. 3(a), a first etching mask pattern 18 corresponding toa first photomask pattern obtained by using a operational result of acomputer is formed on a silicon crystal substrate 14 serving as theoptical substrate. The etching mask pattern 18 can be formed byperforming selective exposing processing and developing processing usingthe first photomask pattern on a photoresist material made from, forexample, a resist TSMR™ manufactured by Tokyo Oka Kogyo in Japan, whichhas been uniformly put on the silicon crystal substrate 14 so that itsthickness is, for example, 1.8 μm.

Next, reactive ion etching (RIE) processing using an etching gas suchas, for example, SF₆ (sulfur hexafluoride) and using the first etchingmask pattern 18 as an etching mask is performed on a surface 14 a of thesilicon crystal substrate 14. By the RIE processing, as shown in FIG.3(b), a surface area of the silicon crystal substrate 14 being exposedoutside the first etching mask pattern 18 is removed to a depth of, forexample, 0.5 μm.

After the RIE processing using the first etching mask pattern 18 as theetching mask, as shown in FIG. 3(c), the first etching mask pattern 18is removed, which causes a two-phase lens plane having two surfaceheight levels to be formed on the silicon crystal substrate 14. Then, asshown in FIG. 3(d), the resist material 19 made from the same materialas described above is formed in a manner that it covers all the lensplanes. The same exposing and developing processing as described aboveusing a second photomask pattern (not shown) obtained by using acomputer is performed on the resist material 19. By the developingprocessing, as shown in FIG. 3(e), a second etching mask pattern 19 a isformed so that each of portions of the lens plane having the two heightlevels is partially exposed.

By the same selective etching using the second etching mask pattern 19 aas described above, a area of the surface portions 14 a of the siliconcrystal substrate 14 being exposed outside the second etching maskpattern 19 a is removed to a depth of, for example, 0.25 μm. After thesecond selective etching processing, as shown in FIG. 3(f), the secondetching mask pattern 19 a is removed, which causes four-phase lens plane10 a having four surface height levels to be formed on the surface 14 aof the silicon crystal substrate 14. Moreover, in FIG. 3, to simplifythe drawing, the illustration of one half portion seen from a centerline L of one circular lens plane 10 a is omitted.

Thus, the processing described in FIG. 1 is performed on the siliconcrystal substrate 14 on which many lens planes 10 a are formed in orderto separate each of the microlenses 10 each having each lens plane 10 afrom the silicon crystal substrate 14.

Second Embodiment

In the first embodiment, as shown in FIG. 1(c), the etching to a desireddepth D can be implemented by the single etching processing using themask pattern 15 a. However, if an etching to a comparatively large depthD being, for example, 200 μm is required, it is desirous that the sameetching processing as described above is repeated, as shown in FIGS. 4and 5.

That is, as shown in FIG. 4(a), by the method explained in FIG. 3, manylens planes 10 a are formed on the surface 14 a of the silicon crystalsubstrate 14. A diameter of each lens plane 10 a is, for example, about123 μm, as described above.

After the formation of the lens plane 10 a, as shown in FIG. 4(b), amask pattern 15 a having a diameter being slightly larger in size thanthat of the lens plane 10 a is formed so as to cover the lens plane 10a.

The mask pattern 15 a may be made from silicon dioxide. The mask pattern15 a can be formed as follows. That is, first, the silicon dioxide witha thickness of 1 μm is stacked by, for example, a CVD (Chemical VaporDeposition) method on the surface 14 a of the silicon crystal substrate14. Then, the same photoresist as used in the first embodiment is put onthe silicon dioxide layer. By performing exposing and developingprocessing on the photoresist, an etching mask is formed. A selectiveetching processing using the etching mask is performed on the silicondioxide layer to form the mask pattern 15 a. To perform etching on thesilicon dioxide, an anisotropic etching gas containing, for example, CF₄and O₂ are used.

After the formation of the mask pattern 15 a, as shown in FIG. 4(c),using the mask pattern 15 a as an etching mask, the surface 14 a of thesilicon crystal substrate 14 is etched to a depth of, for example, 1 μm.In this etching, an etching gas exhibiting an anisotropic characteristicto silicon such as, for example, SF₆ is used.

By the etching processing using the etching gas, under each of thesemask patterns 15 a each having the diameter being slightly larger thanthat of the lens plane 10 a, a cylindrical portion 10-1 containing thelens plane 10 a and having a height d1 of about 1 μm is formed, as shownin FIG. 4(c). A face surrounding each of the cylindrical portions 10-1has an arc-shaped concave curved surface in its cross sectional viewalong a center axis of the cylindrical portion.

When the height d1 of the cylindrical portion 10-1 is about 1 μm asdescribed above, an angle θ formed by a tangential line of the concavecurved surface at a rising portion of the cylindrical portion 10-1 andby a flat surface 14 a of the silicon crystal substrate 14 is 87.5°being near to 90°. A maximum diameter of the cylindrical portion 10-1 is125 μm at its both ends.

After the formation of the first cylindrical portion 10-1, as shown inFIG. 4(d), a protecting film 20 made from a polymer of C₄F₈(octalfluorocyclobutane) is formed which covers an entire surface of themask pattern 15 a, the cylindrical portion 10-1 under the mask pattern15 a, and the silicon crystal substrate 14. This protecting film 20 canbe formed by a plasma reaction of the C₄F₈.

In a state in which portions surrounding a wall of the cylindricalportion 10-1 are covered by the protecting film 20, the surface of thesilicon crystal substrate 14 is etched by etching processing using theanisotropic etching gas such as the described SF₆ (sulfur hexafluoride).Since the portions surrounding the wall of the cylindrical portion 10-1are covered by the protecting film 20, a surface of the silicon crystalsubstrate 14 existing under the protecting film 20 is further etched bythe etching processing, as shown in FIG. 5(a), a cylindrical portion10-2 having a concave surrounding face defined by the same concavecurved surface as the cylindrical portion 10-1 has, is formed seriallyunder the cylindrical portion 10-1.

Moreover, the protecting film 20 is formed in the same manner asdescribed above, as shown in FIG. 5(b), which covers the surface of thesilicon crystal substrate 14 and the concave surrounding face of thecylindrical portion 10-2 both being exposed by the above etchingprocessing.

After the formation of the new protecting film 20 covering portionssurrounding the cylindrical portion 10-2, the next etching processingusing the anisotropic etching gas such as the SF₆ gas is performed onthe surface of the silicon crystal substrate 14.

After processes of a new formation of the protecting film 20 coveringportions surrounding faces of the cylindrical portion being newlyexposed and further formation of new cylindrical portions by the etchingprocessing under the protecting film having been repeated, as shown inFIG. 5(c), the protecting film 20 is removed finally. As a result, thelens element portion (10) consisting of many cylindrical portions 10-1to 10-n being serially formed and having a desired thickness D andhaving the lens plane 10 a at its end is formed.

Each of the lens element portions (10) is separated as the individualmicrolens 10 after the removal of the mask pattern 15 a by the sameprocesses as those explained in FIG. 1(d) to FIG. 1(f). A surface of themicrolens 10 having been formed by repeated processes including theformation of the protecting film covering portions surrounding thesurface of the cylindrical portion being exposed and the new formationof cylindrical portions by the subsequent etching processing under theprotecting film, is of an outer shape having serially repeated concavecurved surfaces, as shown in FIG. 5(c).

Third Embodiment

FIGS. 6 and 7 show a method for forming a microlens 10 by using an SOI(Silicon On Insulator) substrate. The SOI substrate 34, as is wellknown, is made up of a silicon substrate layer 34 a, a silicon dioxidelayer 34 b, and silicon surface layer 34 c. In the embodiment, themicrolens 10 is formed in the silicon surface layer 34 c having athickness of 50 μm to 100 μm.

As shown in FIG. 6(a), many lens planes 10 a are formed on the siliconsurface layer 34 c at regular intervals. Next, though not shown in thedrawings, the plurality of mask patterns 15 a each covering each of lensplanes 10 a are formed by the same step as shown by FIG. 1(b) of themethod in the first embodiment, then a surface area of the siliconsurface layer 34 c being not covered by these mask patterns 15 a eachcovering each of the lens planes 10 a is etched. In this selectiveetching processing on the silicon layers, since the silicon dioxidelayer 34 b functions as an etching stopper, as shown in FIG. 6(b), thesilicon dioxide layer 34 b, even if it is exposed, is not etched much.

Therefore, at a time when the silicon dioxide layer 34 b is exposed, theetching processing is stopped. Since the mask pattern (15 a) (not shown)has been removed at this point, as shown in FIG. 6(b), specified lenselement portions (10) can be left in a comparatively easy manner.

Each of the lens element portions (10) existing on the silicon dioxidelayer 34 b is coated with a wax material 16 as shown in FIG. 6(c), andeach of the lens element portions (10) is supported by a supportsubstrate 17 through the wax material 16 as shown in FIG. 6(d).

When residual portions of the SOI substrate 34 are dipped into, forexample, hydrofluoride acid liquid, with each of the lens elementportions (10) being supported by the support substrate 17, the silicondioxide layer 34 b is removed and, as a result, as shown in FIG. 6(e),each of the lens element portions (10) only is left on the supportsubstrate 17 through the wax material 16.

Therefore, as in the first embodiment, by dissolving the wax material 16in the same solvent as used described above, each of the lens elementportions (10) can be separated from the support substrate 17, whichenables many microlens 10 to be collectively formed.

As described above, by using the SOI substrate to form the microlens 10,each of the lens element portions (10) formed in the silicon substratelayer 34 a of the SOI substrate 34 using the etching liquid can beseparated from the silicon substrate layer 34 a being bonded to the lenselement portions (10) through the silicon dioxide layer 34 b andtherefore a polishing process to be performed on the silicon crystalsubstrate 14 required to separate each of the lens element portions (10)is made unnecessary. Moreover, the separated silicon substrate layer 34a, since it does not undergo the polishing process, can be re-used asthe silicon substrate layer 34 a of the SOI substrate.

As shown in FIG. 7, an antireflection film may be formed, if necessary,on both sides of the microlens 10.

As shown in FIG. 7(a), while each of the lens element portions (10) isbeing held through the wax material 16 by the support substrate 17, aTiO₂ (titanium dioxide) film may be formed on an end face 10 b placed onan opposite side of the lens plane 10 a of the lens element portion (10)by using, for example, a vacuum evaporation system. The TiO₂ film may beformed by a sputtering method, instead of the vacuum evaporation method.

Then, as shown in FIG. 7(b), an UV resin layer 21 is applied in a mannerthat it covers an end face of each of the lens element portions (10) onwhich the antireflection film has been formed. Then, as shown in FIG.7(c), a second support substrate 22 made from a silica material isplaced to contact directly with the UV resin layer 21. The UV resinlayer 21 is irradiated with ultraviolet (UV) light through the secondsupport substrate 22.

When the UV resin layer 21 is cured by the irradiation of theultraviolet (UV) light, a cured portion 21′ being the cured UV resinlayer 21 is formed. The lens element portions (10) are held through thecured portion 21 by the second support substrate 22. The UV resin layer21 and the second support substrate 22 forms a support means.

When the wax material 16 is removed, as described in first embodimentabove, the first support substrate 17 is simultaneously removed and, asa result, the lens element portions (10) are fixed through the curedportion 21′ on the second support substrate 22 in a manner that the lensplanes 10 a of the lens element portions (10) are exposed, as shown inFIG. 7(d).

On each of the lens planes 10 a is formed the antireflection film in thesame way as used in the formation of the antireflection on the end face10 b being positioned on the opposite side of the lens plane 10 a. Afterthe formation of the antireflection film on both sides of the lenselement portions (10), the cured portion 21′ is removed by using thesolvent, which causes the lens element portions (10) to be separatedfrom the second support substrate 22. As a result, the microlenses 10with the antireflection film being formed on both the sides of each ofthe microlenses 10 can be collectively formed.

It is apparent that the present invention is not limited to the aboveembodiments but may be changed and modified without departing from thescope and spirit of the invention.

For example, in the first embodiment, each of the microlenses 10 isproduced by separating the lens element portion (10) from the siliconcrystal substrate 14, however, the microlens 10 may be produced bycreating a replica of the lens element portion (10) using the siliconcrystal substrate 14 with many lens element portions (10) formed thereinas an original and then separating the lens element portion (10) fromthe replica.

To produce this replica, a mold made from, for example, a syntheticresin material is prepared using the silicon crystal substrate 14 withmany lens element portions (10) formed as the original. Then, using themold, the replica of the original is produced and the same polishingprocessing using the support substrate 17 as employed in the processesexplained in FIG. 1(d) to FIG. 1(f) is performed on the replica toseparate the lens element portions (10) from the produced replica and,as a result, many microlenses 10 can be obtained from the lens elementportions (10).

Moreover, in the embodiments described above, the example of themicrolens 10 made up of the diffractive optical element using thediffraction phenomenon in which the lens plane is formed on its one faceis explained, however, the lens plane may be formed on both the faces ofthe microlens 10 if necessary. Also, the present invention may beapplied not only to the microlens 10 made up of the diffractive opticalelement but also to the microlens made up of the refractive-type opticalelement, and the lens plane may have a desired shape and the microlensesmay have a desired outer shape.

Furthermore, manipulating parts other than the lens plane which are usedto facilitate handling of the microlens may be integrally formed ifneeded.

What is claimed is:
 1. A method of forming a plurality of microlenses,comprising the steps of: forming a plurality of lens planes on onesurface of an optical substrate; forming a plurality of mask portionsrespectively covering each of said lens planes; forming lens elementportions which has said lens plane and becomes said microlensrespectively under each of said mask portions by an etching processconducted on said optical substrate; removing all said mask portions;holding said lens element portions by a holding means from the side saidone surface of said optical substrate is located; removing a remainderof said optical substrate excluding said lens element portions forleaving said lens element portions by a removing process; eliminatingsaid holding means from all said lens element portion by a eliminatingprocess.
 2. The method for forming the plurality of microlensesaccording to claim 1, wherein said etching process is a etchingprocessing to etch an exposure area portion being not covered by saidmask portions.
 3. The method for forming the plurality of microlensesaccording to claim 1, wherein said etching process contains a etchingprocessing to etch an exposure area portion being not covered by saidmask portions for forming a part of each said lens element portion, aforming processing to form a protecting film covering a wall surroundingface of said part formed by said etching processing, and a film removingprocessing to remove said protecting film after completing said lenselement portions by conducting said etching processing and said formingprocessing repeatedly.
 4. The method for forming the plurality ofmicrolenses according to claim 1, wherein said etching process isconducted by using etching gas exhibiting an anisotropic etchingcharacteristic.
 5. The method for forming the plurality of microlensesaccording to claim 1, wherein said optical substrate is made up of acrystal substrate.
 6. The method for forming the plurality ofmicrolenses according to claim 5, wherein said crystal substrate is asilicon crystal substrate, said removing process is polishingprocessing.
 7. The method for forming the plurality of microlensesaccording to claim 1, wherein said optical substrate has a silicon layerhaving said one surface and providing a thickness in correspondence witha length of said microlens, and a silicon dioxide layer fixed on saidsilicon layer, said removing process is a dissolving processing todissolve said silicon dioxide layer.
 8. The method for forming theplurality of microlenses according to claim 1, wherein said opticalsubstrate is a SOI substrate consisting of a silicon layer having saidone surface and providing a thickness in correspondence with a length ofsaid microlens, a silicon dioxide layer fixed on said silicon layer, anda silicon substrate layer fixed on said silicon dioxide layer, saidremoving process is a dissolving processing to dissolve said silicondioxide layer.
 9. The method for forming the plurality of microlensesaccording to claim 1, wherein said holding means consists of a waxmaterial layer used to fill the space between said lens element portionsand covering all said lens element portions, and a holding substratefixed on said wax material layer, said eliminating process is adissolving processing to dissolve said wax material layer.
 10. Themethod for forming the plurality of microlenses according to claim 1,wherein said microlens is a diffractive optical element, said lens planeis a lens plane of said diffractive optical element.
 11. The method forforming the plurality of microlenses according to claim 1, moreovercomprising the steps of: forming a antireflection film on each of endfaces of all said lens element portions which is located on an oppositeside of said lens plane after finishing said removing process; using asupport means to support all said lens element portions from the sideall said end face are located on which said antireflection film isformed before conducting said eliminating process; forming aantireflection film on said lens planes of all said lens elementportions after finishing said eliminating process; and removing saidsupport means from all said lens element portions by conducting asupport means eliminating process.
 12. The method for forming theplurality of microlenses according to claim 11, wherein said supportmeans has a support substrate to support all said lens element portionsthrough UV(Ultraviolet) resin layer, said support means eliminatingprocess is a dissolving processing to dissolve said UV resin layer.